Little is known about the etiology or risk factors for autism, a disease affecting 1 in 50 children in the U.S. While genetic and environmental factors are thought to act together, the specific mechanisms are not known and the measurement of environmental risk factors during critical periods of neurodevelopment has been lacking. This case-control study seeks to apply a novel dental biomarker of early life metal exposure, including in utero, to identify risk factors for ASD. Beyond looking at exposure intensity, we will be able to identify differences in exposure timing between cases and controls. This will allow us to identify critical windows when exposure, even at low levels, increases the risk of ASD. Using the proposed biomarker, we will directly assess fetal exposure, and will not rely on maternal biomarkers which may only provide an indirect measure of fetal exposure to metals. This work will have substantial impact on epidemiologic investigations of the relation of early life chemical exposures to ASD and other neurodevelopmental disorders as it can be used to objectively reconstruct both exposure intensity and timing.